Search found 107 matches

by Rishi
Fri Nov 13, 2015 7:37 pm
Forum: Development
Topic: ZX81 / AMIGA music on... tapes / cassettes :)
Replies: 21
Views: 2824

Re: ZX81 / AMIGA music on... tapes / cassettes :)

Found mine but haven't had time to connect it yet
by Rishi
Tue Oct 20, 2015 12:21 pm
Forum: Development
Topic: My new 1K demo
Replies: 22
Views: 2863

Re: My new 1K demo

Works perfectly on my Unmodified zeddy, Great, hmmm this is also proof that there is still something not quite right with my RAM-pack regarding WRX-compatibilty, i don't have time atm to solve this, but at least i do have a perfect tester !
by Rishi
Tue Oct 06, 2015 10:04 pm
Forum: Hardware
Topic: Custom 64K RAM expansion for the ZX81
Replies: 9
Views: 2432

Re: Custom 64K RAM expansion for the ZX81

Very... Nice... Work !
by Rishi
Tue Oct 06, 2015 9:48 am
Forum: Hardware
Topic: Memopak : bad RAM chips ?
Replies: 96
Views: 13282

Re: Memopak : bad RAM chips ?

The schematic in this post isn't actually the latest version, this is : Thx for that... and ouch! I won't even try to figure out what that circuit does! :mrgreen: It's not all that different from the other one, just /REFSN making sure that the characterset is available from the ROM ??? All i am doi...
by Rishi
Mon Oct 05, 2015 11:14 pm
Forum: Hardware
Topic: Modifying a Sinclair ZX81 issue 1 - RAM
Replies: 1
Views: 605

Re: Modifying a Sinclair ZX81 issue 1 - RAM

Nice work Mark !
by Rishi
Mon Oct 05, 2015 8:37 pm
Forum: Hardware
Topic: Custom 64K RAM expansion for the ZX81
Replies: 9
Views: 2432

Re: Custom 64K RAM expansion for the ZX81

Keep me updated on your progress, the /RAMCS in this schematic seems to refer to /CE on the SRAM, if you're putting it on the edge, then /RAMCS should always be high, (A16 on the RAM either high or low, but consistent) /REFSN could also be wired in with /RD, it should effectively give you 56K RAM. S...
by Rishi
Mon Oct 05, 2015 12:06 pm
Forum: Hardware
Topic: Memopak : bad RAM chips ?
Replies: 96
Views: 13282

Re: Memopak : bad RAM chips ?

You're beginning to "get it"... :D Sometimes i do and sometimes i don't, sometimes my info seems a tad incomplete let me see if i understand; if !MI is low, the part of RAM that is addressed should actually always be 4000h - 8000h (regardless of A15) since that is where the D-file is. More exactly:...
by Rishi
Sun Oct 04, 2015 6:26 pm
Forum: Hardware
Topic: Memopak : bad RAM chips ?
Replies: 96
Views: 13282

Re: Memopak : bad RAM chips ?

Ah, maybe i've found a way around (and my earlier mistake) let me see if i understand; if !MI is low, the part of RAM that is addressed should actually always be 4000h - 8000h (regardless of A15) since that is where the D-file is. In other words, the chip should only be disabled(and the other disabl...
by Rishi
Sun Oct 04, 2015 1:37 pm
Forum: Hardware
Topic: Memopak : bad RAM chips ?
Replies: 96
Views: 13282

Re: Memopak : bad RAM chips ?

Anyway, what i don't get is that my IO-port can disable the SRAM via !CE (if the A2-A15 are high and !MI and !(!MEMRQ) ) so the SRAM gets disabled for addresses FFFCh-FFFFh but when i do that for just A15 and !MI and !(!MEMRQ) then something goes wrong. Of course i have to keep disabling it in case ...
by Rishi
Sun Oct 04, 2015 9:38 am
Forum: Hardware
Topic: Memopak : bad RAM chips ?
Replies: 96
Views: 13282

Re: Memopak : bad RAM chips ?

Hmm, I try and look for most Datasheets, had some trouble finding the logic table to the multiplexers though, Also in spite of many good efforts, some of the schematics are rather hard to read. One would actually expect that with all the HiRes capabilties and all they would not be made up out of das...